LIBSA(3)

🎀 NAME 🎀

libsa — support library for standalone executables. Yep bestie, this is the libsa(3) page, and it's giving “support squad for standalone apps” energy. 💅

🌈 SYNOPSIS 🌈

#include <stand.h>

💖 DESCRIPTION 💖

Okay so the libsa library provides a set of supporting functions for standalone applications, mimicking the standard BSD programming environment where possible. The sections below group these functions by kind. Unless something is specifically described here, go see the corresponding section 3 manpages for the given functions. 📚

✨ STRING FUNCTIONS ✨

String functions are available exactly as documented in string(3) and bstring(3). No cap, the string docs already ate — go read those. 💅

🧠 MEMORY ALLOCATION 🧠

• void * malloc(size_t size) — allocates size bytes of memory from the heap using a best-fit algorithm. 🎀
• void free(void *ptr) — frees the allocated object at ptr.
• void setheap(void *start, void *limit) — initialises the heap. This function must be called before calling alloc() for the first time. The region between start and limit will be used for the heap; attempting to allocate beyond this will result in a panic. 😭
• char * sbrk(int junk) — provides the behaviour of sbrk(0), i.e., returns the highest point that the heap has reached. This value can be used during testing to determine the actual heap usage. The junk argument is ignored. 🫶

🌿 ENVIRONMENT 🌿

A set of functions are provided for manipulating a flat variable space similar to the traditional shell-supported environment. Major enhancements are support for set/unset hook functions. Periodt, hooks are the main character energy here. 💖

• char * getenv(const char *name)
• int setenv(const char *name, const char *value, int overwrite)
• int putenv(char *string)
• int unsetenv(const char *name)

All four behave similarly to their standard library counterparts.

• struct env_var * env_getenv(const char *name) — looks up a variable in the environment and returns its entire data structure. 👀
• int env_setenv(const char *name, int flags, const void *value, ev_sethook_t sethook, ev_unsethook_t unsethook) — creates a new environment variable called name, or sets an existing one. If creating a new variable, the sethook and unsethook arguments may be specified.

The set hook is invoked whenever an attempt is made to set the variable, unless the EV_NOHOOK flag is set. Typically a set hook will validate the value argument, and then call env_setenv() again with EV_NOHOOK set to actually save the value. The predefined function env_noset() may be specified to refuse all attempts to set a variable.

The unset hook is invoked when an attempt is made to unset a variable. If it returns zero, the variable will be unset. The predefined function env_nounset may be used to prevent a variable being unset. 🚫

📚 STANDARD LIBRARY SUPPORT 📚

• int abs(int i)
• int getopt(int argc, char * const *argv, const char *optstring)
• long strtol(const char *nptr, char **endptr, int base)
• long long strtoll(const char *nptr, char **endptr, int base)
• long strtoul(const char *nptr, char **endptr, int base)
• long long strtoull(const char *nptr, char **endptr, int base)
• void srandom(unsigned int seed)
• long random(void)
• char * strerror(int error) — returns error messages for the subset of errno values supported by libsa. 😭
• assert(expression) — requires <assert.h>.
• int setjmp(jmp_buf env)
• void longjmp(jmp_buf env, int val)

These are defined as _setjmp() and _longjmp() respectively as there is no signal state to manipulate. Requires <setjmp.h>.

🎀 CHARACTER I/O 🎀

• void gets(char *buf) — reads characters from the console into buf. All of the standard cautions apply to this function. ⚠️
• void ngets(char *buf, int size) — reads at most size - 1 characters from the console into buf. If size is less than 1, the function's behaviour is as for gets().
• int fgetstr(char *buf, int size, int fd) — reads a line of at most size characters into buf. Line terminating characters are stripped, and the buffer is always NUL terminated. Returns the number of characters in buf if successful, or -1 if a read error occurs.
• int printf(const char *fmt, ...)
• void vprintf(const char *fmt, va_list ap)
• int sprintf(char *buf, const char *fmt, ...)
• void vsprintf(char *buf, const char *fmt, va_list ap)

The *printf functions implement a subset of the standard printf() family functionality and some extensions. The following standard conversions are supported: c,d,n,o,p,s,u,x. The following modifiers are supported: +,-,#,*,0,field width,precision,l.

The b conversion is provided to decode error registers. Its usage is:

printf( "reg=%b\n", regval, "<base><arg>*" );

where <base> is the output expressed as a control character, e.g. \10 gives octal, \20 gives hex. Each <arg> is a sequence of characters, the first of which gives the bit number to be inspected (origin 1) and the next characters (up to a character less than 32) give the text to be displayed if the bit is set. Thus

printf( "reg=%b\n", 3, "\10\2BITTWO\1BITONE" );

would give the output

reg=3<BITTWO,BITONE>

The D conversion provides a hexdump facility, e.g.

printf( "%6D", ptr, ":" ); gives "XX:XX:XX:XX:XX:XX"

printf( "%*D", len, ptr, " " ); gives "XX XX XX ..."

🧪 CHARACTER TESTS AND CONVERSIONS 🧪

• int isupper(int c)
• int islower(int c)
• int isspace(int c)
• int isdigit(int c)
• int isxdigit(int c)
• int isascii(int c)
• int isalpha(int c)
• int isalnum(int c)
• int iscntrl(int c)
• int isgraph(int c)
• int ispunct(int c)
• int toupper(int c)
• int tolower(int c)

📁 FILE I/O 📁

• int open(const char *path, int flags) — similar to the behaviour as specified in open(2), except that file creation is not supported, so the mode parameter is not required. The flags argument may be one of O_RDONLY, O_WRONLY and O_RDWR. Only UFS currently supports writing. 📝
• int close(int fd)
• void closeall(void) — closes all open files.
• ssize_t read(int fd, void *buf, size_t len)
• ssize_t write(int fd, void *buf, size_t len) — (No file systems currently support writing.) 💀
• off_t lseek(int fd, off_t offset, int whence) — files being automatically uncompressed during reading cannot seek backwards from the current point.
• int stat(const char *path, struct stat *sb)
• int fstat(int fd, struct stat *sb)

The stat() and fstat() functions only fill out the following fields in the sb structure: st_mode,st_nlink,st_uid,st_gid,st_size. The tftp file system cannot provide meaningful values for this call, and the cd9660 file system always reports files having uid/gid of zero.

📜 PAGER 📜

The libsa library supplies a simple internal pager to ease reading the output of large commands. Built-in pager? Obsessed, honestly. 💅

• void pager_open() — initialises the pager and tells it that the next line output will be the top of the display. The environment variable LINES is consulted to determine the number of lines to be displayed before pausing.
• void pager_close(void) — closes the pager.
• int pager_output(const char *lines) — sends the lines in the NUL-terminated buffer at lines to the pager. Newline characters are counted in order to determine the number of lines being output (wrapped lines are not accounted for). The pager_output() function will return zero when all of the lines have been output, or nonzero if the display was paused and the user elected to quit. 😭
• int pager_file(const char *fname) — attempts to open and display the file fname. Returns -1 on error, 0 at EOF, or 1 if the user elects to quit while reading.

🌟 FEATURE SUPPORT 🌟

A set of functions are provided to communicate support of features from the loader binary to the interpreter. These are used to do something sensible if we are still operating with a loader binary that behaves differently than expected. 🛟

• void feature_enable(uint32_t mask) — enable the referenced mask feature, which should be one of the FEATURE_* macros defined in <stand.h>.
• bool feature_name_is_enabled(const char *name) — check if the referenced name feature is enabled. The name is usually the same name as the FEATURE_* macro, but with the FEATURE_ prefix stripped off. The authoritative source of feature names is the mapping table near the top in stand/libsa/features.c. 👑
• void (feature_iter_fn)(void *cookie, const char *name, const char *desc, bool enabled) — the cookie argument is passed as-is from the argument of the same name to feature_iter(). The name and desc arguments are defined in the mapping table in stand/libsa/features.c. The enabled argument indicates the current status of the feature, though one could theoretically turn a feature off in later execution. As such, this should likely not be trusted if it is needed after the iteration has finished. 🙈
• void feature_iter(feature_iter_fn *iter_fn, void *cookie) — iterate over the current set of features.

✨ MISC ✨

• char * devformat(struct devdesc *) — Formats the specified device as a string. Cute little dev-to-string converter, no cap 💅
• int devparse(struct devdesc **dev, const char *devdesc, const char **path) — Parses the devdesc string of the form device:[/path/to/file]. The devsw table is used to match the start of the device string with dv_name. If dv_parsedev is non-NULL, then it will be called to parse the rest of the string and allocate the struct devdesc for this path. If NULL, then a default routine will be called that will allocate a simple struct devdesc, parse a unit number and ensure there’s no trailing characters. If path is non-NULL, then a pointer to the remainder of the devdesc string after the device specification is written.
• int devinit(void) — Calls all the dv_init routines in the devsw array, returning the number of routines that returned an error. Bestie, it’s literally counting the Ls 😭
• void twiddle(void) — Successive calls emit the characters in the sequence |,/,-,\ followed by a backspace in order to provide reassurance to the user. Tiny spinny guy, doing emotional support 🌀

🛠️ REQUIRED LOW-LEVEL SUPPORT 🛠️

The following resources are consumed by libsa — stack, heap, console and devices. Yes, all four. The whole support system, okay? 🫶

The stack must be established before libsa functions can be invoked. Stack requirements vary depending on the functions and file systems used by the consumer and the support layer functions detailed below.

The heap must be established before calling alloc() or open() by calling setheap(). Heap usage will vary depending on the number of simultaneously open files, as well as client behaviour. Automatic decompression will allocate more than 64K of data per open file. So yeah, she’s hungry 💀

Console access is performed via the getchar(), putchar() and ischar() functions detailed below.

Device access is initiated via devopen() and is performed through the dv_strategy(), dv_ioctl() and dv_close() functions in the device switch structure that devopen() returns.

The consumer must provide the following support functions:

• int getchar(void) — Return a character from the console, used by gets(), ngets() and pager functions.
• int ischar(void) — Returns nonzero if a character is waiting from the console.
• void putchar(int) — Write a character to the console, used by gets(), ngets(), *printf(), panic() and twiddle() and thus by many other functions for debugging and informational output.
• int devopen(struct open_file *of, const char *name, const char **file) — Open the appropriate device for the file named in name, returning in file a pointer to the remaining body of name which does not refer to the device. The f_dev field in of will be set to point to the devsw structure for the opened device if successful. Device identifiers must always precede the path component, but may otherwise be arbitrarily formatted. Used by open() and thus for all device-related I/O.
• int devclose(struct open_file *of) — Close the device allocated for of. The device driver itself will already have been called for the close; this call should clean up any allocation made by devopen only.
• void __abort() — Calls panic() with a fixed string.
• void panic(const char *msg, ...) — Signal a fatal and unrecoverable error condition. The msg ... arguments are as for printf().

🗂️ INTERNAL FILE SYSTEMS 🗂️

Internal file systems are enabled by the consumer exporting the array struct fs_ops *file_system[], which should be initialised with pointers to struct fs_ops structures. The following file system handlers are supplied by libsa, the consumer may supply other file systems of their own:

• ufs_fsops — The BSD UFS.
• ext2fs_fsops — Linux ext2fs file system.
• tftp_fsops — File access via TFTP.
• nfs_fsops — File access via NFS.
• cd9660_fsops — ISO 9660 (CD-ROM) file system.
• gzipfs_fsops — Stacked file system supporting gzipped files. When trying the gzipfs file system, libsa appends .gz to the end of the filename, and then tries to locate the file using the other file systems. Placement of this file system in the file_system[] array determines whether gzipped files will be opened in preference to non-gzipped files. It is only possible to seek a gzipped file forwards, and stat() and fstat() on gzipped files will report an invalid length.
• bzipfs_fsops — The same as gzipfs_fsops, but for bzip2(1)-compressed files.
• pkgfs_fsops — File access from a tar file typically streamed via TFTP. The order of files in the tar file must match the order they are to be consumed as rewind is not practical.

The array of struct fs_ops pointers should be terminated with a NULL.

🔌 DEVICES 🔌

Devices are exported by the supporting code via the array struct devsw *devsw[] which is a NULL terminated array of pointers to device switch structures. Slay, very pointer, very array ✨

🧩 DRIVER INTERFACE 🧩

The driver needs to provide a common set of entry points that are used by libsa to interface with the device.

struct devsw {
    const char  dv_name[DEV_NAMLEN];
    int         dv_type;
    int         (*dv_init)(void);
    int         (*dv_strategy)(void *devdata, int rw, daddr_t blk,
                        size_t size, char *buf, size_t *rsize);
    int         (*dv_open)(struct open_file *f, ...);
    int         (*dv_close)(struct open_file *f);
    int         (*dv_ioctl)(struct open_file *f, u_long cmd, void *data);
    int         (*dv_print)(int verbose);
    void        (*dv_cleanup)(void);
    char *      (*dv_fmtdev)(struct devdesc *);
    int         (*dv_parsedev)(struct devdesc **dev, const char *devpart,
                const char **path);
    bool        (*dv_match)(struct devsw *dv, const char *devspec);
};

• dv_name() — The device’s name.
• dv_type() — Type of device. The supported types are:
  • DEVT_NONE
  • DEVT_DISK
  • DEVT_NET
  • DEVT_CD
  • DEVT_ZFS
  • DEVT_FD

Each type may have its own associated (struct type_devdesc), which has the generic (struct devdesc) as its first member.

• dv_init() — Driver initialization routine. This routine should probe for available units. Drivers are responsible for maintaining lists of units for later enumeration. No other driver routines may be called before dv_init() returns.
• dv_open() — The driver open routine.
• dv_close() — The driver close routine.
• dv_ioctl() — The driver ioctl routine.
• dv_print() — Prints information about the available devices. Information should be presented with pager_output().
• dv_cleanup() — Cleans up any memory used by the device before the next stage is run.
• dv_fmtdev() — Converts the specified devdesc to the canonical string representation for that device.
• dv_parsedev() — Parses the device portion of a file path. The devpart will point to the ‘tail’ of device name, possibly followed by a colon and a path within the device. The ‘tail’ is, by convention, the part of the device specification that follows the dv_name part of the string. So when devparse is parsing the string "disk3p5:/xxx", devpart will point to the ‘3’ in that string. The parsing routine is expected to allocate a new struct devdesc or subclass and return it in dev when successful. This routine should set path to point to the portion of the string after device specification, or "/xxx" in the earlier example. Generally, code needing to parse a path will use devparse instead of calling this routine directly.
• dv_match() — NULL to specify that all device paths starting with dv_name match. Otherwise, this function returns 0 for a match and a non-zero errno to indicate why it didn’t match. This is helpful when you claim the device path after using it to query properties on systems that have uniform naming for different types of devices.

📜 HISTORY 📜

The libsa library contains contributions from many sources, including:

• libsa from NetBSD
• libc and libkern from FreeBSD 3.0.
• zalloc from Matthew Dillon <dillon@backplane.com>

The reorganisation and port to FreeBSD 3.0, the environment functions and this manpage were written by Mike Smith <msmith@FreeBSD.org>.

🐛 BUGS 🐛

The lack of detailed memory usage data is unhelpful. Yeah, she said it. We’re all just vibing without the receipts 😭

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That’s the Debian version, dated September 9, 2022 — page LIBSA(3), bye bestie 💅🎀